In order to optimize production from existing wells, it is often desirable to re-enter the wells and, after milling a window in the well casing, sidetrack the well into better reservoir rock. Further, directional drilling to provide multi-lateral well bores from an existing main bore hole has become increasingly popular in many formations.
In sidetracking and directional drilling of multi-lateral wells, coiled tubing offers many benefits, including faster mobilization and demobilization, faster trip times, continuous circulation during tripping, smaller footprint, less site preparation and remediation.
However, one of the limitations of using coiled tubing in casing milling is that the torque available at the bit, i.e., the milling tool, is limited to the output of the torque of a downhole motor. Thus, unlike techniques for casing milling using conventional wellbore drilling or servicing rigs, in the use of coiled tubing, because of torque limitations, the rate of penetration into the casing wall is more likely to stall than in use of conventional methods.